Known in the prior art is a titanium-type catalyst comprising a titanium compound and an organoaluminum compound or a vanadium-type catalyst comprising a vanadium compound and an organoaluminum compound, for use in the production of an olefin (co)polymer including an ethylene homopolymer and ethylene/.alpha.-olefin copolymers.
Further, a Ziegler catalyst for olefin polymerization comprising a zirconium compound and an organoaluminum oxy-compound (aluminoxane) is also known as a catalyst which can be used for producing an olefin (co)polymer with a high polymerization activity, and a process for preparing an ethylene/.alpha.-olefin copolymer using such catalyst is proposed in, for example, Japanese Patent Laid-Open Publications No. 19309/1983, No. 35005/1985, No. 35006/1985, No. 35007/1985 and No. 35008/1985. Moreover, a process for polymerizing an olefin using a catalyst formed from a mixture of a zirconium compound and an organoaluminum compound consisting of aluminoxane and an organoaluminum compound is proposed in Japanese Patent Laid-Open Publications No. 260602/1985 and No. 130604/1985.
In the presence of such a catalyst comprising the zirconium compound and the organoaluminum oxy-compound, olefins can be polymerized with a high polymerization activity. However, there is such a problem in the case of using the organoaluminum oxy-compound that, since the compound is generally prepared by causing an organoaluminum compound to react with water and this reaction process is complicated, the compound becomes expensive and, therefore,.the cost for preparing an olefin (co)polymer also becomes high.
On that account, eagerly desired now is the advent of a catalyst for olefin polymerization which comprises a zirconium compound and an organometallic compound other than the organoaluminum oxy-compound and which is excellent not only in the olefin polymerization activity but also in the economical efficiency. Further, the advent of a process for polymerizing an olefin using such a catalyst is also desired.
As such a catalyst for olefin polymerization, for reference, a catalyst comprising a transition metal compound, a Lewis acid and an organoaluminum compound is proposed in Japanese Patent Laid-Open Publication No. 179005/1991.